Commenting on the deal, NSM Insurance Group CEO Geof McKernan said: “White Mountains brings NSM strong financial backing and a long-term view of the business which will enable us to continue our organic and acquisition growth strategies both in the US and UK.”

White Mountains CEO Manning Rountree said: “We are pleased to make this investment in NSM alongside the management team. The company is high quality and we believe there is tremendous opportunity to grow and expand the business.

“We look forward to working with Geof and his team, and to providing them with support and resources to continue to grow the business organically and through acquisitions.”

Subject to regulatory approvals and other customary closing conditions, the transaction is scheduled to be completed by the end of the second quarter of 2018.